The present invention generally relates to the art of data communications and telephony. More particularly, the invention relates to a plain old telephone system (POTS) device, or a device that operates in connection with the Public Service Telephone Network (PSTN), for example but not limited to, a telephone, facsimile machine, analog modem, caller ID system, speaker phone, cordless phone, etc., that employs an on-board POTS filter to enable reliable and efficient decoupling of a POTS channel from one or more xDSL channels on a telephone connection, while reducing interference imposed upon the xDSL channels.
Recently, in the art of telephony, 2-wire copper telephone connections have been utilized for communicating more than one simultaneous communications channels, such as digital data and analog voice signals. For example, a high speed digital subscriber line (XDSL, e.g., asymmetric DSL (ADSL), symmetric DSL (SDSL), rate adaptive digital subscriber line (RADSL), very high speed ADSL (VADSL), etc.) channel and a plain old telephone system (POTS) channel can be established over a single physical 2-wire connection. The signals are typically separated in frequency. The POTS channel usually exhibits a frequency spectrum of about 0 KHz to about 4 KHz, whereas the XDSL channels exhibit a frequency spectrum of about 20 KHz to about 500 KHz.
A POTS splitter, also known as a POTS filter, a telephone filter, a microfilter, or a CP (customer premises) filter, has traditionally been utilized to decouple the channels, or separate the POTS channel from the other channels, due to non-linearities inherent in most, if not all central office powered telephones. The POTS filter is usually implemented in series with the telephone in order to reduce the DSL power imparted on the telephone electronics, which imposes interference upon the POTS and the DSL signals.
A POTS splitter is typically a passive or active one-to-two port device. The POTS splitter is installed between a telephone jack and the telephone itself and is also connected to a DSL device. It includes a POTS filter (a one-to-one port device) situated between the telephone line and the telephone that is designed to minimize high frequency transients produced by on-hook/off-hook transitions, so as to prevent tainting or slowing of the high speed data on the DSL channel. Also, it is usually configured to provide a high impedance to the telephone line in the DSL frequency band in order to prevent DSL power from being imparted on the POTS communications device that is connected to the line. In essence, the filter reduces incident DSL signal power to reduce DSL signal intermodulation (IMD), which undesirably creates audio noise heard in the receiver of a telephone, and interferes with the DSL signal.
Because of the foregoing requisite functionality, POTS splitters are usually expensive devices and are oftentimes installed on a physical wall of a customer premises (CP), such as on an outside wall of a building. Furthermore, generally, POTS splitters require installation by a skilled telephone company worker, not the premise owner, resulting in undesirable installation time, labor, and expense. Distributed microfilters per phone are an increasingly used alternative to the outside wall splitter for the reason cited.
The specification of POTS splitters and filters has been the subject of several industry standards bodies. For example, see American National Standards Institute, ANSI T1.413-1995, Sections 8 and 10, regarding ADSL/POTS splitters. Moreover, as an example of a possible implementation of a POTS splitter, see J. Cook, P. Sheppard, xe2x80x9cADSL and VADSL Splitter Design and Telephony Performance,xe2x80x9d IEEE Journal on Selected Areas in Communications, December 1995.
Commonly assigned U.S. Pat. No. 5,848,150 to T. J. Bingel, who is also one of the inventors herein, describes a passive one-to-one port POTS filter for enabling decoupling of a first channel, such as a POTS channel, from a second channel, such as an xDSL channel, that is communicated simultaneously with the first channel on a telephone connection, while permitting and not appreciably interfering with the second channel. The POTS filter can be connected between the telephone jack and a telephone or can be situated within the telephone. Each POTS filter has a passive automatic control mechanism and a passive first channel filter (e.g., a POTS filter). The automatic control mechanism is configured to isolate the first channel filter when a respective first communications device is inactive (on-hook). Further, the distributed filter is configured to interface communications on the first channel (e.g., POTS channel) on the telephone connection with the respective first communications device when the first communications device is active (off-hook). Moreover, a second communications device (for example, a modem) is connected to the telephone connection and communicates signals over a second channel (xDSL, e.g., ADSL, SDSL, RADSL, VADSL, etc.), simultaneously with the first channel. As a result of the invention, an inexpensive passive distributed filter system associated with the POTS channel prevents on-hook/off-hook transitions from interfering with the second channel communications.
Although meritorious and effective to an extent, the passive distributed filter system implements a control mechanism, and it would be desirable to implement such a filtering function with less complexity and requisite circuitry. Furthermore, the filter usually contains inductors in series with the telephone line and capacitors in parallel with the telephone. The presence of these reactive elements introduces concerns about excessive POTS attenuation, reduced PSTN network stability, poor telephone sidetone, increased ringer loading, and degraded termination impedance, especially with multiple telephones on the telephone line (a typical scenario). Thus, a heretofore unaddressed need exists in the industry for an improved filtering systems and methods.
The present invention provides a plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., that employs an on-board POTS filter to enable reliable and efficient decoupling of a POTS channel from one or more XDSL channels on a telephone connection, while permitting and not interfering with the XDSL channels. In general, the POTS filter is situated after the telephone connection switch (for example, a hook switch). The switch effectively isolates the POTS filter from the telephone line when the POTS device is disconnected, or is xe2x80x9con hook,xe2x80x9d and interfaces the telephone line through the POTS filter to the POTS transmitter, receiver, or transceiver when the POTS device is connected, or is xe2x80x9coff hook.xe2x80x9d
In architecture, the POTS device, which connects to a subscriber loop associated with the public service telephone network (PSTN), includes a subscriber loop connection switch (for example, a hook switch), POTS electronics (including a transmitter, receiver or both (transceiver)), and a low pass filter (LPF) interconnecting the subscriber loop connection switch with the POTS electronics. The switch effectively isolates the POTS filter from the telephone line when the POTS device is disconnected, or is on hook, and interfaces the telephone line through the POTS filter to the POTS electronics when the POTS device is connected, or is off hook. The arrangement enhances DSL device performance, network stability, sidetone, ringer load, and termination impedance and allows greater flexibility in the choice of filter elements, in that passive and active elements can be utilized and in that filters of higher order can be employed.
The invention can also be conceptualized as providing a method for a POTS device that is connected to a subscriber loop. Broadly stated, the method can be summarized by the following steps: coupling a subscriber loop connection switch to a POTS transmitter, receiver, or transceiver; and filtering out high frequency signals from voice band signals communicated between the loop connection switch and the transmitter, receiver, or transceiver.
The invention has numerous advantages, a few of which are delineated hereafter, as merely examples.
An advantage of the invention is that it provides a way of achieving telephone XDSL compatibility without an external CP telephone filter. That is, the invention teaches a method for telephone manufacturers to design and produce DSL compatible telephones.
Another advantage of the invention is that it can be used in any data communication device that connects to a single physical connection having at least two communications channels (e.g., a high speed xDSL link in combination with a POTS link), where the channels are separated by frequency, and that includes a telephone line connection/disconnection switch (such as a hook switch).
Another advantage of the invention is that it can be used to effect economical deployment of a XDSL communications channels simultaneously in combination with a POTS communications channel on a telephone connection.
Another advantage of the invention is that it is simple in design, efficient in operation, and easily and economically implemented and manufactured on a mass scale.
Another advantage of the invention is that passive components, active components, or a combination of both can be utilized in the filter.
Another advantage of the invention is that it is very desirable for typical homeowners and consumers in that it does not require sophisticated installation.
Another advantage of the invention is that it meets surge and safety requirements of industry standard UL1950, Third Edition, and applicable requirements of FCC, Part 68.
Other systems, methods, features, and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included herein within the scope of the present invention and protected by the claims.